Re: [TUHS] FreeBSD behind the times? (was: Favorite unix design principles?)

Dave Horsfall <dave(a)horsfall.org> writes: [snip] I have some real world experience with ZFS and bad blocks. As mentioned by others, compression is not required, but it would not matter too much. ZFS is somewhat odd in that you can mount and use a damaged filesystem without too much trouble and recover anything possible. A real example (and to keep it a TUHS topic), we had an older Solaris 10 Sparc at the $DAYJOB about two years ago that developed bad blocks on the drive (ZFS detected this for us). Not a surprise given the age of the system, being 6 to 8 years old at the time, we replaced the drive without issue and started a re-silver (ZFS's version of fsck and raid rebuild) and during that re-silver another drive developed block errors. This was a RAIDZ1 set up, so having two drives go out at the same time would cause something to be lost. If it were another RAID variant, it would probably have been fatal. What ZFS did was told us exactly which file was effected by the bad block and the system kept going, no unmounts, reboots or down time. We replaced the second drive and the only problem we had was a single lost file. Compression would not have changed this situation much, except perhaps making the problem a bit bigger, we may have lost two files or something. I have another example with a Sun NFS appliance that runs under the covers Solaris 11 that developed multiple drive fails. In the end, we estimated that around 40% or so of the multi terabyte filesystem was damaged. It was possible to still use the appliance and we were able to get a lot off of it as it continued to function as best as it could you just could not access the files that had bad blocks in them. ZFS has honestly been amazing in the face of the problems I have seen. -- Brad Spencer - brad(a)anduin.eldar.org - KC8VKS - http://anduin.eldar.org